Forensic Trace Chemistry – Flashcards

because otherwise you will get thermal noise from the MCT detector

-Detector on main bench is DTGS and doesn't have the same problem

• electrocoat (25 micro)
• primer (25-40 micro)
• basecoat (13-25 micro)
• effect coat
• clear coat (35-50 micro)

• 25 micros
• offers rust protection for steal
• usually from local suppliers

• 25-40 micros
• thick layer of material which provides a very smooth surface to enhance the quality fo the paint job and appearance
• usually from local suppliers

• 13-25 mciros
• the color of the car
• usually from major suppliers, mostconsistent

• 35-50 micros
• provides additional protection for the basecoat and gives it a "depth"
• older cars did not have a clear coat
• usually from local suppliers

• polymer forming materials that provide the basis for the bulk of material
• polyesters, acrylics, polyurethanes

• polymer forming material that will form the structure of the paint and gives hardness and durability
• melamines, isocyanates

• UVAs= UV absorbing compounds which are colorless and the main purpose is to absorb UV rays to protect the organic pigments of the color coat
• acrylics, UVAs

• vehicle
• cross-linkers
• pigments
• additives

• Pittsburg Paint and Glass
• one of the three major suppliers

• German COmpany
• one of three major paint suppliers

• main paint supplier for the world

• Bumper paint is different than OEM/body paint because it must be more flexible and the surface is made of plastic substrates
• Technology varies from plant to plant
• waterborn (low volatiles)
• pigments are suspended in water
• Solvent borne
• 1K vs 2K
• powder primer and clear coats
• color

• K= kit
• 1K is premixed in the paint gun, more stable
• 2K has two diff pain supplies which are mixed as they go through teh paint gun

• have virtually no solvents in them
• can be applied electrostatically

• Solvent Borne 1K
• polyester/melamine in US
• polyester/CAB/melamine in europe
• Waterborne
• polyurethane/polyester/acrylic/melamine
• Pigmentation
• varies by supplier and customer preferenace
• majority of new cars are silver (14 diff silvers)

• 1K (less reactive)
• acid/epoxy
• acrylic/polyol/melamine
• 2K
• urethane from isocyanate/polyol reaction
• starts to react as soon as htey come in contact
• low shelf life
• Melamine/HydroxylXlink
• trans-esterification reaction where blocking group is replaced by the polymer
• can get a 3D reaction
• reacts to form a solid fill
• Carbamate/Melamine Xlink
• 3D cross-linking, carbamate linkage
• Isocyanate/Hydroxyl Xlink
• isocyanate becomes a urethane
• Rest is solvent borne PE/melamine

• distinguishable by IR
• clearcoat cna differentiate paints which appear to be thesame color
• Ceramiclear
• Carbamate
• Acid/Epoxy liquid
• Acrylic Silane
• Standard 2K isocyanate
• "High Tech" Clear
• Water Clear

• clearcoat unique to Mercedes 2K iso since late 2002
• contains nanoparticulate silica
• detectable with SEM, NOT detectable with LOM
• more expensive and durable coating

• isocyanates are more reactive
• both in NA and Europe

• acrylic/melamine with blocked iso fortification
• primarily high-end european cars

• acrylic/blockiso/melamine
• priamrily in california

• Dupont product only
• low level of silicon in acrylic
• more flexibility and increased chip resistsance
• found on bumpers

• Pigmentation often unique to specific color
• problem is that suppliers can change rapidly from year to year
• chemistry is complex
• will depend on what the vehicle (film forming molecule)is
• polyester/polyurethane/acrylic/melamine
• water/solvent
• relativelysmallamount of pigment invehicle
• particularly with organic compounds because they are very intense

• BMW mini is trying to cut down on costs of painting by eliminating primers if electrocoat is sufficient or maybe a little thicker
• increasing plastic parts allows for less primer

1. body panels welded together then sanded
2. cleaned of oils and dirt
3. metal"passivated" with phosphoric acid dip
1. improve adherence of primers
2. adds somerust protection
4. electrocoat primer-rust protection
5. primer/surfacer-gives smooth surface
6. basecoat-primary color
7. effect coat-metallic, pearlescent,custom
8. clear coat- chip restistance, UV protection of color, improves depth

• if inspection in plant reveals imperfection in paint after bake, it is sanded out and a new basecoat/clearcoat is applied
• it is then rebaked
• migration of pigment into lower clearcoat during rebake can occur
• repaints at repair shops have different chemistries because they cannot be baked

• diffusion out of a permeable film due to high V gradient
• traps water molecules which diffuse out as high voltage gradient occurs (squeezing out the water)

• ppt of paint particles at an electrode
• charged paint micelle migrates toward and then coagulates on an electrode
• Cathodic:;positive charged paint moves toward neg. cathode
• make car negative relative to the paint molecules
• Aniodic: neg. charged paint moves toward pos. charged anode
• as the paint builds up, the paint itself becomes non-conductive and the currend drops, end up with a very uniform layer of paint

• acid functional polyers neutralized with organic amines
• used melamine or alkyd drying reactions for crosslinking
• Positives:;low cost of materials (vs. cathodic), color control if Fe dissolution is controlled
• Negatives:;attack on substrate during deposition (particularly Fe)
• formaldehyde released in cure -formula dependent
• melamine gives off formaldehyde as a byproduct
• drift in pH of bath due to Co2 uptake
• traps acid at meatl/paint interface
• useful on aluminum body parts (vs. steel)

• two classes of polymers currently used
• amine functional polymers neutralized with organic acid/sulfamic acid
• sulfonium functional polymers with organic acid counter ion
• cured with blocked isocyanates
• most widely used process in auto industry
• increases corrosion protection
• superior chemical resistance
• improved gloss and color retention
• non-staining on Fe substrates
• imporved detergent resistance
• better throwpower/rate of coverage

• cost effective utilization of paint
• theoretical 100% of the paint particles going on the body
• no overspray
• high quality appearance and film properties
• uniform thickness
• superior corrosion performance
• adherence to present and future environmental regs

• NOT for corrosion resistance
• enhances chip resistance
• low build for areas where appearance is most important (top, hood, trunk lid)
• high build (thicker layer) for areas where chip resistance is needed (Bumpers, fenders, side panels, bottom)
• provides smooth surface for basecoat
• provides UV protection for electrocoat layer
• primarily aliphatic rather than aromatic resin

• decoration= provides main color, smoothness
• protection;
• corrosion resistance
• chip resistance
• chemical resistance
• moisture resistance

• silver is most common (40% in NA and 80% in Eur)
• black, blue, red distant
• white is more common than black
• high end mercedes/BMW mostly silver
• 12 different types of silver for Mercedes;

• aluminum powder
• mica
• micronized TiO2
• graphite flake
• colored Al
• Glass flake
• Opt. Var. Pigments (differnt angles show diff color)
• synthetic mica

• rapid heaitng of high molecular weight organic causes fragmentation into smaller molecules that can be analyzed
• destructive technique but very small sample sizes needed
• fragmentation can be fairly predictable and reproducible with proper control of pyrolysis conditions
• GC often used to separate pyrolysates ;(most will be in gaseous form)

• Random Scission
• Side Group Scission
• Monomer Revision

• breaking apart of carbon backbone of long-chain molecule into smaller molecules of varying size
• if all C-C bonds are of same energy, then breaking any given bond is random
• Polyolefins do this
• give wide distribution of compounds over a fairly wide range of molecular weights (and thus a wide range of elution time in GC)
• will find a homologous series of triplets and within each group is a diene, a monounsaturated and a saturated compounds

• chlorine in PVC are elimintated as HCl leaving a polyunsaturated backbone (left with an olefin)
• backbone undergoes further scission with rearrangement into aromatics
• benzene, toluene and napthalene are usual products

• nylon
• also called depolymerization
• primary products are monomers similar to monomers used to make polymer in first place
• C-C bonds of the backbone are the weakest and beta scission with unzipping back to monomer gives rise to most stable free radical
• R group has little effect
• Copolymers generally rise to products in proportion to amount of each monomer

• Microfurnace
• Curie Point
• Resistive Filament

• held at constant temp
• sample drops/injected into heated zone
• poor heat transfer to sample
• poor separation of products to large volume inlet
• instead of a nice sharp band, might get broad peaks at the detector
• standard split/splitless injector

• temperature at which it loses its magnetic susceptibility
• RF coil rapidly heats sample in ferromagnetic boat to curie temp of alloy
• if you put alloy in a coil and oscillate it fast enough it will cause the atom to flip in the alloy to rise rapidly until it reaches the curie point (loses susceptibility and will no longer flip) and it loses its magnetic properties
• making a boat of this alloy can allow for it to heat up right at the specified temperature of its curie point
• limited number of alloys limites temp choices
• same kind of effect as in ICP

• gives the most flexibility
• platinum coil/ribbon which works like a platinum resistance thermometer
• resistance of platinum is proportional to temp
• rate and final temperature can be controlled by electronics
• heating curves can be customized for application
• limited sample size for efficient heat transfer
• similar to graphite AA
• put sample inside quartz tube which slides into coil and whole thing is put inside apparatus
• heat up just the tip
• continuously flushed with helium so effective volume is much less than previous methods
• cools down very quickly, little thermal mass
• problem is that you must be careful putting quart tube in filament
• not used routinely

• GC w/ FID
• separates volatiles by BP, molecular size and/or functional groups
• mostly for "fingerprinting" samples
• FTIR
• either directly after pyrolysis (good for Mon.Rev) or after GC separation (for more complex mix)
• chemical ID of products
• MS
• either directly after pyrolysis or after GC
• chemical ID;
• particularly useful if a derivative method is used

• H2 carrier gas over Pt or Pd catalyst
• reduces unsaturated bond formation
• reduces carbonization of sample (which happens a lot during pyrolysis)
• used with polyethylene and similar polyers, things broken by random scission
• microfurnace type pyrolyzer
• more compound produced, cleaner material, better separation and ID

• Rxn with TMAH (tetramethylammonium hydroxide) during pyrolysis
• methylates polar sites on fragments
• improves GC separation
• useful for natural products and Polyester type synthetics that would undergo monomer revision

• fibers;
• complimentary to microIR and PLM
• NOT good for dyes
• Paint (binders mainly)
• Inks
• Fats and Oils (stains)
• Polymers (good for insolubles)
• Adhesives
• Artistic Materials
• Bioterrorism (bacterial cells, anthrax)

• Animal, Vegetable, Mineral

• wool, silk, hair, fur
• protein chains with (standard) peptide linkages
• visible microscopic exam can distinguish between different types based on hair structure

• Seed(cotton, Kapok)
• derived from fibers surrounding seeds
• cotton is most common
• mainly cellulose but includes other plant components
• Bast (flax, hemp, ramie)
• derived from teh stem or stalk of the plant
• bast is the stalk material
• Flax= 75% cellulose, 15% hemicellulose, 2% lignin
• Leaf (sisal), derived from leaf material

• vegetable;
• plant frequently mixed with cotton materials

• Have a lot of distinguishing chemical characteristics that you can detect in IR
• Synthetic Polymers:;totally synthetic polymers=polyolefins, polyesters
• Natural Polymers:;chemically processed material of natural origin (rubber, rayon, acetate)
• also glass, carbon, metallic, etc

• Monomer containing double bonds added together at double bond to form polymer
• degree of polymerization is very high
• generally most stable polymers becuase C-C bond offers no site for cleavage
• polyolefins will generally melt
• handle is the "feel"lf it, addition polymers tend to feel soft and waxy

• monomers contain two reactive groups which can link by condensation reaction to form linear polymers
• lower degree of polymerization than addition type
• less stable because linkage is typically ester or amide bond
• susecptible to hydrolysis by acids or alkalis, will reverse reaction and you'll be left with an amine and a carboxylic acid

• polyester
• nylon
• polyurethane
• kevlar

• extraction protocol depends on type of fiber
• TLC of extract helpful in classification of dyes
• HPLC or CEC for further comparison
• jeans and cotton fibers might not be as useful because they are so common/ubiquitous (want to look more for unique fibers)

•  an inorganic transition metal that binds the dye to the structure of the material

• samples prepared to 5-15 micro thickenss by rolling with a roller knife
• use a diamond compression cell
• place specimen between two optically flat faces and tighten down to compress
• ideally leave it in cell, find sample, and do transmission

• many fibers are basically round in cross section and if your aperture approaches 2x the wavenumber of the fiber in the IR region, you get diffraction patterns

• Sample Too Thick
• absorbance of the strongest band will be greater than 1.5
• band shapes are distorted and band ratios incorrect
• can fix by making sample thinner and compressing
• Interference Fringes
• associated with sample thickness
• common with diamond cell, especially when using both windows (air gap between windows)
• can fix by melting a small bead of fiber and compress to fill view, by using only 1 window, or by putting  asmall piece of KBr in cell with fiber, compress and use as a background
• Sample Too THin
• absorbance less than 0.3 for strongest bnad
• weak bands lost in noise
• increasing number of scans can help by decreasing noise
• redoing sample is best if possible

• Acid (wool, nylon, silk)
• Pre-Metallized(wool, Nylon, Cotton
• Reactive (Wool, Nylon, Cotton)

• physical evidence is any tangible object are brought into court and formally submitted as evidence

• small size of material
• vestige as in something left behind as a result of exchange or interaction

• Non-Contact
• generally more useful in reconstruction
• BPA and GSR
• Independent of Transfer
• Static Contact Deformation: indentation evidence, fingerprint impressions
• Dynamic Contact Deformation: bullet striations, tool marks, one surface moving relative to another
• Fracture Matches: ends of tape, torn paper, broken glass

• Elemental
• Glass, bullet fragments
• XRay
• ICP-AES
• ICP-MS
• NAA
• EDAX-SEM
• Molecular
• paint, fibers, explosives, inks, GCMS, FTIR,etc

• security screening at airports or other potential targets
• smuggling or theft of explosives
• locating unexploded devices following bomb threat
• primary method is x-ray for device components
• vapor detection for explosives themsleves (nitro groups)

• commonly used at airports
• GC with the thermal energy analyzer (TEA) detector or IMS detector
• dry wipe of exterior of carry on baggage
• wipe is inserted into a heated zone where explosive particles vaporized and swept into GC
• looking for vapors from explosive particles which went from person's hands to baggage
• separated, specific detector with alarm
• needs little training to operate

• part of EGIS
• sample swpet into area where ozone is added and reaction of ozone with nitrous oxides will give off a photon of light;
• nitrogen compounds are oxidized to NO2* + O2
• NO2* decays NO2 with emission of photon (detected)
• also called a chemiluminescene detector
• looking for hte marker compound in plastic explosives (NOT RDX/C4)
• Disadvantage is that it doesn't detect peroxide based explosives

• moderately volatile components added to low volatile, high explosives to aid in detection pre-blast (primarily) and post-blast
• EGDN: ethylene glycol di-nitrate (explosive itself)
• DMNB: 2-3 dimethyl, 2-3-dinitrobenzene
• not explosive itself, but somewhat more volatile than RDX and is comparable to TNT and some of the others
• well resolved from other components
• MNT: ortho and para mononitrotoluene
• RDX is not detectedbecause it is a low volatile compound and doesn't volatilze int he heated zone

• particles adhering to body are detected with a stream/puff of air to blow a few particles off
• not very effective

• collection of evidence (everything that looks like it might be related)
• device components
• pipes, fuses, det cord,adhesives, shock tubing, wires, blasting caps, etc
• signature of bomber can be used to relate one explosive event with another
• explosive residue and extent of explosion
• can backtrack and figure out how much of hte actual explosive was used to leave that effect/residue

• During visual exam you are looking for device pieces
• during microscopic exam, look for particle which look like they might be explosive materials
• elemental sulfur is soluble in organicsolvents and will give a very distinctive GC peak and spec
• PLM is pretty good, older method
• IC good for separating anions and cations
• swab pieces with organic solvent and also a water solvent and get extracts from those
• combo of size and shape of smokeless powder can get you down to a brand or a few brands
• combo of GC or HPLC can get you maybe all the way down to box or lot

• initial testing of intact suspected low explosives to determine if they will support combustion
• used to differentiate from non-explosive debris
• black powder, pyrodex, smokeless powder,pyrotechnic mixtures (fireworks)
• burn a particle on a spatula using an alcohol flame, if it flashes it is porbably an explosive!

• initial testing of suspected intact and explosive residue
• water extract of sample (mainly inorganics)
• colors and/or crystalline precipitate
• acetone or methanol extract for organics

;

• DPA
• Griess 1 and 2
• Anilate Sulfate
• Sodium Azide
• TPS Chloride
• BaCl2/HOAc
• AgNO3/NH4OH

• anion test for explosives
• diphenylamine
• Oxidizers (except ClO4)

• anion test for explosives
• Nitrate (NO3) and Nitrite (NO2)
• used for potential GSR on shooters (back in the day)
• modified version still used for distance determination/GSR

• anion test for explosives
• chlorate (ClO3)

• anion test for explosives
• perchlorate (ClO4)
• distinguish perchlorates from chlorates
• blackpowder substitutes and some IED
• chlorate and aluminum powder make good explsives

• anion test for explosives
• carbonate (CO3) and sulfate (SO4)
• not as useful because there can be a lot of these in the environment (?)

• Nessler
• K Paper/HNO3
• Zn Uranyl Acetate
• NaOH/dil HOAc/Morin
• Pyrimidine/NaOH

• cation test for explosives
• ammonium (NH4)
• alkaline metals and ammonium ions don't precipitate very well, use others

• cation test for explosives
• potassium 
• source o fnitrate material can be important, want to distinguish KN and NaN

• initail testing of suspected intact explosive residues
• presumptive test for NG distinguishes between SB and DB smokeless powders (SB= 1 spot, DB= 2)
• Solvent is 4:1 hexane/acetone for smokeless powders of 56:37:7 toluene/cyclohexane/diformamide for resolving NG and EGDN
• spray with KOH in ethanol followed by heating
• spray with Greiss I and Griess II
• look at color changes and retention times, compare contorls

• inorganic ions-CEC or IEC
• IEC of anions-presence of perchlorate indicates it is one of the smokeless powder substitute
• organic residues
• GCTEA or MS with Cl or MSMS
• nitro containing compounds have a high electron affinity and can form negative ion under chemical ionization conditions and use that to detect and accentuate the nitro compounds
• HPLC-DAD
• CEC-DAD or MS

• perchlorate, chlorates, sulfates, nitrates
• perchlorate indicates it is a SP substitute
• amount of sulfate present means its not one that is completely sulfur free
• elemental sulfur product is sulfate

• find chlorats, nitrates, nitrites, chloride (always there), thiocyanate ions (biproduct), benzoate (indicator of pyrodex)

• performed on organic extract
• traditional EI modeleads to extensive fragmentation of many explosives
• inlet temp, ion trape can degrade  NG
• positive or negative ion chemical ionization (Cl or NCl) are more useful
• can do SIM

• usually DAD detection but ECD and MS have been used
• reverse phase msot commonly used
• organic extracts of debris

• trouble detecting non-volatile components (like RDX)
• biggest problem is with the wiping of the pad-if you don't collect the particles from the item they won't be detected

• expose layers using oblique (5 deg.) angle with sharp scalpel
• clean blade between layers
• remove small portion of layer and flatten with roller or diamond cell
• leave in diamond cell or transfer to AgCl disk
• AgCl is transparent to infrared, can do a transmission type experiment

• micropellet with CsI instead of KBr
• thin filmon AgCl
• Diffuse Reflectance

• instead of KBr
• alternative to AgCl disk
• grind up sample with small amount of CsI and make 1 mm pellet
• beam condenserand standard FTIR bench (DTGS detector)
• has lower wavenumber limit than MCT which is useful for inorganic pigments which absorb below 650 nm

• SiC paperto sample single layer or smear
• can be used with either Diff Reflectance accessory or microscope
• common with architectual pain which often has a few thick layers

• CsI goes down to 200
• wide range of MCT detector will go down to around 450
• characteristic bands are usually higher up

• paint resin
• used in older lacquer repaint fillers and undercoatings
• lacquer coatings on tools
• detected with DPA test (dark blue color)
• found primarily in repaints, not used as much anymore

• polyvinyl chloride and polyvinyl acetate
• used in interior and exterior house paints due to low cost
• architectural paints-easy water clean up paints
• IR peak ID flow chart
• carbonyl bands present from the PVA

• low cost materials added to add bulk or opacity to hte aterial/pigment
• aluminum, silicats, magnesium

• primarily green to yellow color
• many are below 650 nm, won't be seen with our detector
• cannot distinguish with microscope
• must use micropellts on an extended range bench

• the common white pigment, added to a lot of other colors/pigments

• centralized database of auto OEMfinishes updated and expanded by end user contributions
• basedin Canada but supported in US by FBI
• approx 1/3 or samples directly from manufacturers
• contain source of sample along with color, chemical composition, and layer sequence in paint system
• general, text based search system (not spectrum search)
• elimintates instrument dependencies
• has a coding system

• microfurnace and curie point;
• larger samples
• can be for composite or single layer
• Pt Resistance (CDS type)
• small samples required
• ideal for sampels of individual layers
• Complimentary to FTIR